Automatic volume control



Jan. 1, 1935. Af PFlsTER 1,986,644

I AUTOMATIC VOLUME CONTROL Filed sept. 24, 19:51 4 sheets-sheet 1 ggd ARTHUR PFISTER BY A/f MM ATTORNEY Jan. l, 1935. A. PFls'rER 1,986,644

AUTOMATIC VOLUME CONTROL Filed sept. 24, 193,1v 4 sheets-sheet 2 ARTHUR PFISTER ATTORNEY Jan. l, 1935. A. PFlsTER AUTOMATIC VOLUME CONTROL Filed Sept. 24, 1951 4 Sheets-Sheet 3 lNvENToR ARTHUR PFlSTER BY NL@ q ATTORNEY Jan. l, 1935. A. PFls'rER AUTOMATIC VOLUME CONTROL Filed Sept, 24, 1931 4 Sheets-Sheet 4 INVENTOR ARTHUR PFISTER I BY ATTORNEY Patented Janel, 1935 PATENT 'orme anroivm'rlc voLUMEvooN'rRoL l ,Arthurristen Maspeth, N. y., assigner to nadie CorporationgoffAmerca,a corporation oi. D ela- Ware i Applnation;` sente i This invention relates to the-radio art 'and more in particular to a novel means to be used incommunication for automatically controlling the 'aniL plitude, volume; or level of lsignals atanyfre'quen be used in radio communication.

.i cies, Iand in particular 'to `frequericies "may Due tothe limitations imposed .byeiiistingcom` munication lines, input equipment, and'terminal equipment, itis necessaryto bring alli@ resulting Vlo level variations) in' the signal` in thein.c'orrect{prow-Q` portion to each other; and to: hold themwithinthe permissible dynamicv` range? fof" the"` transmission line or signalconveying medium. ,To do so necessitates thefuse ofL "a volume "control. i,

or compressinga dynamic Vrange ina-transmission line means insuring that theamplitude of"rtl'iesig-` nalsin the line is less by an amount which'varies' over the entire range than thesignals'irnpressed 30` ated. Trained operators are required'lto'compress on the line.` `lilicpanding a dynamicfrange a transmission line means insuring that Lthe ampli; tudeof theH signals in the line'is greaterby an amount which varies over the :entire range.Y than M' "if thesignals impressedonthelineli.l'\ i Volume controls have been known heretofore. i With volume controls i known heretofore it has"` been the practiceQto accomplisw 'controlof` the signal `amplitude by manually 'operatedi'devices exclusively. Suchv devices known heretofore in-f volved step-by-step'attenuators `and'':oritinuously variable faders, both of `which are manuallyoper-- signals of an initially :wide *"dynamicfrange into signals' ofia range considerably narrower" without distorting!` their character." 1 Moreover," in *the 'i event that high quality'musical transmission his' involved,` the operator `must have' ai4 thorough knowledge of the particularlselectionthe `isl`con` trolling to be capableofanticipatinganysudden level changes `and meetthem withhisl` controls, that is, the controls connected with the-step-bystep attenuators, or continuously 'variablefaders The primary object of the presentA invention is to provide meansfor'compre'ssing in afnew and|` improved manner by a new andfiinproved means- "fist e provide means; asindicated inithc two' preceding.

the signals within a predetermined dynamic range.

Another object. .of the i present :invention is`l` tol` provide means, `as `indicated above, which, when slightly adjusted,` `will expandV lthe transmitted `signals within a predetermineddynarnic rangei Another object of thepresent` invention is to` paragraphs, whichfis novel but ksimpvi'e'rin"mature `and entirely automatic-in operationrt i i A` further object' kofi the` present@inventionlis to provide means cooperating with 'theoutput-fof said transmission line to restore the control sig-` nalsresultingfrom the compression orexpansion within a predetermined "dynamic range to their original volume or to any desired volume.`

Numerous other objectsfand advantagesto bev gained bythe use ofthe present invention will appear hereinafter. `No attempt beenmade to list the objects of the present inventionin order of their importance. i 1

i Briey, these objects are attained by the use of a thermionic attenuator arranged in symmetrical circuits and including variable` means for conftrolling 'the compressive or expansive percentage regulation. The attenuator stageis connected on thecne hand withthe output `of the signalsource on the other hand to an ampliiier whichfre-` stores the amplitude tothe desired amount'.5v Gontrol means for the attenuator is provided; C This cntrolmeelns includes means forfconverting signals into unidirectional biasing voltages which areV utilized to`` effect the impedance` change in the thermi'eic attenuators in the symmetrical attenuatorcircuit. 'lhisstage may be connected with 2 the signal input brieflydescribedabov` or with a separate signalN input. [Filterimeansfare interposed between;` the last `f'described control means andthe attenuator.` The ,filter means includes inertial circuits anda second means for regulate ing.v the percentage ofV attenuation or control inl'niarted"by.` the attenuator to the signal relayed therethrugh. V Y 'hatl consider `the novel features of" my inventionhave been` pointed out with more par-4 i `on the dynamic range of any signals and any` frequency to beztranslated;` l Figure V2 `illustrates diagrammatically thearrangement of the various units used byapplicant` accomplishing the volume control as `brieiiyV outlined hereinbefore; j Figure `3` rshows diagrar'nrnaticallyV the circuit Y arrangement andthe units of Figure 2; Figure 4 shows a novel broadcast distribution system `including the dynamic rangejcontrol device ofthe present invention; While,

Figure 5 shows an application of the dynamic range control device to a generator and signal modulator system.

Referring to the drawings, and in particular to Figure l1 thereof, the units on the X axis of cent expansive control has beenapplied to the" passing signals. f

In Figure 2, which illustrates.diagrammatically the various stages involved, the signalto be controlled is impressed from any source on stage 1 which comprises the attenuator,` andffrom stage l lis impressed on stage 4 which includes theY amplier which restores the signal to the desired volume. The control signal output from stage 4 is transmitted to any rutilization circuit, as,j for l example, a line,a modulating stage, etc.v

The control signal is impressedkon stage 12,.

which includes rectifying means forconverting the signal j input into unidirectional voltage. Stage 3 includes the lter and inertial circuits which are interposed between therectier and the 'balanced attenuator.

`The circuit arrangement involved in theA vari-` ous stages in the present preferred form ofthe invention'will now bel described'by referenceto The attenuator proper,

Figure 3 of the drawings. or stage 1, is included in a separate compartment inthe metallic closure B, asindicated. This attenuator comprisesa pair ofthermionic tubes 10 and 1-2 and a line L having an input terminal:

at 14 and an'output terminal at 16. Signals are impressed on the lineLfby means of a transformer kT having a primary windingfconnecl',e i. withthe source and asecondary winding 1 8'con,.l

nected across the line L. The cathode 20of the tubes '10 and-12 isk provided with a4 connection `31l which provides ameans for balancingtheftrans-f mission line with respect to ground and the. me# tallic shielded compartment. vThe cathode is en-v ergized by means `of a-sourcenot shown` Thel anode- 22 o-f tube 10 isr connected with one side of the line L, whiie the anode 24 'of tube ,iais

connectedwith the other side of the line L. s This results inr placing` theanode cathode impedance of the two tubes in series across theline. r4Signal oscillations which are not shunted bythe anode cathode impedance of the tubes'l and v12 appear in Athe primary winding 24 o fan outputv transformer OT and are repeated in the second-v ary winding 26 vthereof. The secondary winding.

26 is arranged, as shown, to impress the .signal voltages accumulatively on the potentiometer to beutilizedor further acted on in amanner which will appear more in detail hereinafter.y The primarywinding 24 in the voutput end of the line comprises two. symmetrical portions, as shown. The center tap, or thev midpointv of these'two sections, is connected through a chok-` v n ingfinductanc'e v28 and a variable resistance v`29 to the high potential terminal of the anode power source. -Indicating means, as, for instance, Va milliammeter, Hmay be inserted in this vconnection. Y

y directly.A K l In operation, with equal levels applied to the Attenuatien is" effected by" June shunt arm, that is, by the internal-,impedance of the tubes 10 and,4

12 connected in the full wave circuit across the line. Grid bias variation of these tubes obviously regulates the attenuation since Variation of grid bias varies the internal impedance of the tubes.. The attenuation may be varied within a range determined by the obtainable internal impedance variation of the valves. The resistn ance 2,9 permits variation of the relation `.of grid bias to internal resistance of thetubes.y This variable resistance 29 represents the first of two means for obtaining regulation of, percentage of, control of the dynamic range Within which the signa-l is'he1d.- 1 j i vStage 2 includes the vvmeans for controlling the vbiasing ,v potential applied to the tubes of the This means in' thermionic tubes 1n stage 1. cludes a transformer 30 having a primary circuit separately-connected to the signal source and a lsecondary circuit connected across the diagonals of afull wave rectifier R; The other diagonals of' the full wave rectier R are connected, as shown, to the lter circuit included in stageS. Theunidirectional current'derived from the signal input appears at the input terminals of the ilter stage wherein the current is filtered to obtain pulses more free of alternating current components.. The filter circuit in stagey 3includes a series inductance-32 and parallel condensers 3,4 and 36. `The values of the inductance 32 and the capacities 3 4, 36 are such as to introduce the desired inertial, or' lag,in the filter circuit. The flterjcircuit terminates. in a -variable resistance 38.*-, .'A, normal Vbiasing potential is applied from abiasing source, 40 connected'with the negative terminal ofthe filter circuit on the one hand and through avariaole potentiometer 42 to the negativeterminal of the Asource on the other hand. The frectier, R in stage 2 provides unilateral voltages, jtheamplitudeI of which is characteristic of the amplitude ofthe input signal. Thus, direct current pulsations are filtered in the lter circuit in stage 3 and appliedto the grid of the attenua- Vtor tubes in stage -1 Ato obtain'at the output of the attenuator, a dynamic level of prescribed value corresponding to the input level. The resistance 33V provides the second of thetwo means for obtaining regulation of percentage of control. The inertial andlter circuit of stage 3v converts any rateofamplitude changes occurring in stage 2 intoa resultant average amplitude whose rate of change may. be below audibility' and whose periodicity is being determined by an adjustable timeconstant which utilizes the.. duration of charge and discharge of a condenser through al resistance.A f

The amplifier in stageV 4 is of conventional design and comprises thermionic tube 25 having a control electrode 27 connectedto a point on the potentiometer; 35. Biasingpotential is applied by a source 29. Thegamplier 25'restores the signal derived from-theattenuator to the desiredaverage level. amplifier-stage 25 maybe connectedfwith a transformer, asy indicated,

signal input of stage 1 and the control signalinputof .stage2 :of the automatic volume control of la value-'indicated .by thepoint P on the curves of Figure 1,;it isevident vthat' at this point P no controlling of the signal takes place since the gain of,l stage 4 just compensates for the loss suffered in: stage 1.l All signal levels above orbelow the point `P arebeing'amplied or attenuatedfrespectivelyfby an amount which. de-

The anode circuit of the` or `with a load' circuiti `pends f entirely. upon the' percentage tof" control. which inf' turnris 'the function of zthe attenuator tubecharacteristics and their, plate; current', grid' voltage relations.: .f

In' the case of signal level compressionatlower input levels,` `the 'attenuation decreases; andA aids` the amplification andcconversely at higher` signal input l levels the.. attenuation increases,` thereby opposing the amplicationxlflence, the output variations assume a control. characteristic` `which may well be represented bycurveizgofFigure 11.'

For `signal levelV expansionythefuabove action, is reversed. `'Ihis.Willbe,obviousxlolrl:a `'nspection of'curveBofligu're'l; i: p L .i

Point P may be chosen to lie anywherefalong the `control characteristic curve y withincertain limits. by` initially adjusting by `means of; the rlter circuit l. and. resistancej 38v the nbias applied `=`to :the grids oftheattenuator-,tubestand by adjusting l theresistance 29 inltheoutput circuit ofthe attenuators. and` by adjustinggthe gain control: resistance 2810i the ampliiienstage. l

While it wiubereacny understoodthat rsymel` dynamic range determining deviceor volume lcon-S. trol; may be!used.fin;any@signalling` .Circuitust-1d` today, and at anypointinsaid circuitseithervas adynamic range expanderor as fa dynamicrrange compressor,l I'hava; fori purposes of illustration,

` tem whereinthe Vsignals frompany source, desig.

shown in Figuregl a` preferred broadcasting ar-Y rangement wherein .the-dynam'icrrange control has been utilized.` -ltlyvill'again'berepeatedfthat` this illustration and the illustrations following are Amade merely by,vx wayv `ofillustration,andmet to limit theapplication of. 'said volume control;

' except Vasoutlined `in tiieclaims hereinafter- In Figure ,4 is` illustrated abroadcasting sysnated here signal input,are `passedi through a dynamic range control device acting. asaniauto-` matic compressonas indicated. The signals pass from the last named device to a line and through a switching arrangement to beutilized in either of two manners. When the switch to the left is closed the compressed signals arepassed through a 'transcontinental wire Ycircuit including the necessary repeaters to fan automatic expander which in turn applies the Signals to any utilization circuit. The. automatic compressor come.,

prises the signals within a dynamic range easily `handled by the transcontinental wire circuit.

When the right hand switch is closedthe comi pressed signals are` fed to a radio transmitter where they are amplified if necessary andim` pressed on high frequency carrier waves for transmission. `'I'he radiated waves are received on any absorption structure from which they are fed to a radio receiver as indicated. From `the radio receivers the signals may be passed through an automatic expander and restored totheir original amplitude andfed to any utilization circuit.

The system outlined briefly aboveis especially applicable to short wave transcontinental broadl casting.

In Figure 5 is shown the dynamic? range control interposed betweena source ofsignals and a signal modulator which isk connected on the one hand to a line feeding a utilization circuit, and

. erator.

on the other hand to a carrier frequency gen- The signals from thesignal modulator may be passed over the line to a second dynamic range control or to amplifiers, orto any known utilization circuit. l i m Having thus described my invention and the operation thereof, whatI claim is: l c

1. In signalling devices, a signal transmission une; to be l connected with ianV audible yrreraumcy soul-ce1 and"` means tov attenuate the` signals pass` ing 'oversaid linecomprisinga pair of thermionic vtubes having theirimpedances connected inseries ampliiierj-m'eansfm connecting the secondary;

windings of` said transformers in parallelj and with the input electrodes "of said thermionic ampliena work circuitconnected with the out-` put i electrodes cf\` said amplifier, means (for attenuating `the signals passed over said line corn" pricing, av pair of thermionic tubeshaving their internal=`impedances connected in series across said line, means for balancing saidlineand said attenuatingmeans comprisinga connection between "said thermionic impedances and ground, and 'meansvffor determining` `the :impedance offered by said tubes tosignals owing in `said line comprising, a rectifier, a filter circuit `con-H` nected` between the output electrodes of said rectier and the control" electrodesK of said` attenua* ato'r tubes, and' means connecting the input circuit offsaid rectifle'rito'saidsource of signals. Y

i 3.*"1An`arrangement` as `claimed in claim `2 in:

which, said transmission line` includes a resistance on each '-,si'de thereof, `said rectifier is of'the full wave type, and in 1winch said lter'circuit includes 'a variable resistance;

4. In a broadcasting system comprising, high frequency carrier wave relaying means, a source fof modulatingpotentials, and atransmission line between said modulating potentialsource and said vrelaying means, an automatic `volume control device for attaining a higher average percentage of modulation with a resulting increase in signal Astrength at thereceiver comprising, a pair of thermionictubes each having an anode, cathode and control grid, each tubehaving its anode to cathode impedances connected in series across 'said transmission line, a connection between said impedances and ground whereby said transmission line is balanced, a rectifier having input terminals supplied ,with modulating potentials from said source,` and a filter circuit connected between the output terminals of said rectifier and the control electrodes of said tubes.

5. In *a` broadcasting system including, high frequency carrier wave relaying means, a source of modulating potentials, a transmission line between said modulating potential source and said Vrelaying means', receiving means, signal utilizing means and a transmission line between -said receiving means and saidutilizing means, an .automatic volume control `device in one of said transmission lines for maintaining in said system l'a dynamic rangeof signals to meet certain demands whichcall for a proportionality of the controlledsignal at a certain ratio to theuncontrolled signal comprising, a pair of thermionic triodes," each having its anode connected to a different side of said transmissionline and its cathode connected to'g'round whereby said line is balanced, a rectifier having input' terminals supplied with modulating potentials from said source,a lter circuit connected with the outalityof the controlled signal at a Icertain ratio to the uncontrolled signal comprising, a pair of thermionictriodes for each line, each triode of a pair having itsy anode connected to one side of said transmission lineand their cathodes connected together and to ground wherebysaid lines are balanced, ,a pair of rectiers having input' terminals supplied rwith modulating potentials from said source, a lter circuit connected with the output terminals ofeach of said rectiers, said 'ltercircuits terminating in variable resistances,

and a connection between each of said resistances ,and vthe control electrodes in al different pair of said .triodes '7. In a broadcasting system including,v high frequency carrierv wave relaying means, a source of modulating potentials, a transmission line between said modulating potential source and said relaying means, receiving means, signal utilizing means and a transmission line between said receiving means and said utilizing means, an automatic Vvolumevcontrol device in one of said transmission lines for attaining ahigherfav'e-rage per'-r centage of modulation with a resulting increase -in signal strength at the receiver comprising, a pair of thermionic tubes having their cathodes connected together and their gridsconnected together, means for connecting the anode of each of Vsaidtubes to opposite sides of said transmission line, a rectifier having input terminalssupplied with modulating potentials from said'source, a lter circuit comprisingseries inductances and parallel capacities connected with the output terminals of said rectier,'said lter circuit terminating in a variable'resistance, anda connection between said resistance and the control electrodes s in said tubes.

8. A translating circuit `for conveying audible frequencies from a source of audible' frequency signals to a utilization circuit comprising, a transmi's'sio-nline coupled on the one hand'tosaid source of audible frequencies andon the other hand to saidcircuit, an automatic range determining means in said transmission line for maintaining the signals of audible yfrequency which `flow therein within a certain dynamic range to meet certain demands of said line which call for a proportionality of the signal at a certain ratio to the vuncontrolled signal comprising a pair of thermionic tubes having anode, cathode and control electrodes, circuits for connecting the anode to cathode impedance of lsaid tubes infseries across said line, means for balancing said line with respect-` to ground comprising a connection between the cathodes ofsaid tubes and ground, a

rectier having Vits input terminals connected with said source of audible frequency signals, a filter circuit connected with the output terminals of said rectifier, land a connection between said lter circuit and the control electrodes in each 

